How can I play my IRL friends in expanded format?

I created an old favourite deck so I could play against a friend online, but the game doesn't seem to be letting me. Most of the pokemon in the deck I created are older cards, and therefore banned from standard format. I can use the deck fine when playing 'expanded format with people I don't know. But I don't seem to be able to play expanded format with my friend? Which seems very strange, and quite frustrating. Is there something I'm missing? Thanks!